The airstrip, 20 miles north-west of Porgera, Enga Province, is said to be inaccessible by road.

Mr Allen was expected to be flown from the area by helicopter on Friday morning, local time, and to be put on a plane home on Saturday.

Local time is 10 hours ahead of GMT, but it has not yet been confirmed whether the explorer has actually left the jungle.

Reclusive tribe

Steven Ballantyne, an expedition leader and friend of Mr Allen, told the BBC on Thursday: “What we think is that he travelled much further than he anticipated, that he was going through much tougher terrain than he anticipated.”

He had been travelling on his own to try to find the reclusive Yaifo tribe, whom he first met 30 years ago.

Before setting off, Mr Allen told the BBC he was hoping to make contact with the tribe, who were high up in a cloud forest.

He said he was unsure how they would receive him this time. His last text message read: “What could possibly go wrong?”.

The explorer, from London, has previously crossed the Amazon Basin on foot and in a dug-out canoe, and participated in a six-week male initiation ceremony in which crocodile marks were carved onto his body.

He has filmed a number of his adventures for BBC documentaries and written books on exploration.